High-resolution non-destructive 3D interrogation of dentin using X-ray nanotomography

Objectives Dentin, a calcareous material sandwiched between the pulp and the enamel in the tooth structure contains highly orientated tubules. As a result of enamel erosion, gum recession, physical trauma or caries the dentin tubules can become patent to the oral cavity. It has been demonstrated in vivo that dentinal fluid flows out of the tubule lumen into the oral cavity and it has been postulated that alterations in fluid flow form the basis of dentin hypersensitivity. In order to better understand the mode of action of desensitising occlusion-based agents the ability to interrogate dentin non-destructively is paramount. Destructive analysis of the tooth structure may yield subtle artifacts leading to erroneous conclusions or inhibit the accurate assessment of the relationship between an occluding agent and the internal dentin morphology. This paper describes the use of a novel and accessible, non-invasive, high-focused X-ray computer tomographic technique for analysis of the dentin substructure. Methods Dentin slices, ca. 300 μm3 in size, were taken from the coronal section of unerupted human third molars and etched in citric acid to reveal the open tubule structure. Samples were analyzed, in their dry state, using the Skyscan 2011 nanoCT system. Results Numerous, homogeneously dispersed elliptical features, distinguished by their contrast and hence low-mineral density, were observed. These features are observed to be approximately 2–5 μm in diameter at a density equivalent to 106 cm−2. 2D CT re-slices demonstrate that these circular features form highly orientated cylindrical manifestations extending throughout the sample. Significance Ultra-high-resolution X-ray computed tomography has been shown to be a powerful new technique for interrogating the submicron tubular structure of dentin non-destructively.